THERE are more than 16,000 actors in the Naked City - and seemingly all of them have appeared on TV's "Law & Order."

Well, not quite all.

We refer you to one Christopher Sieber, the erstwhile Sir Dennis Galahad and Black Knight of "Spamalot," whose Playbill bio, bristling with references to off-Broadway plays and TV soaps, concludes, "Mr. Sieber has not appeared on Law & Order."

That was 21/2 years ago - and his record remains gloriously unchanged.

"It's true, it's completely true," says the 37-year-old actor, just back from the show's London production, which he helped open with Tim Curry, the original King Arthur from "Spamalot."

"I'm not bitching and moaning about it, and I'm not hard up for work. But if you look at Playbills, every New York actor has done 'Law & Order,' 'SVU,' or those other letters. Some actors have done all three."

Not that Sieber - who was nominated for a Tony for his triple-threat role in "Spamalot" - hasn't tried.

By his own estimate, he's auditioned for "L&O" about 10 times - sometimes in front of Dick Wolf, the show's creator and producer (who's been quoted as saying that the show's "bible" is "the front page of the New York Post," but that's another story).

"I once went in for a guy who murdered somebody and was getting away with it," Sieber recalls.

"And then there was an airport incident where the baggage handlers were stealing stuff, and I went up for one of the baggage handlers.